1. Field of the Invention
The present invention relates to an optical deflector and an optical scanner including the optical deflector, which are applied to, for example, image formation apparatuses such as a laser printer, a facsimile, and a copier.
2. Description of the Related Art
FIG. 15 shows an example of a conventional optical deflector 310 applied to an image formation apparatus (Japanese Published Unexamined Patent Application No. Sho 63-259510).
In the optical deflector 310, a rotary axis 314 provided with a mirror 312 is fitted to a stationary axis 316, and a thrust magnet 326 mounted on the top end of the rotary axis 314 is disposed between a thrust magnet 318 mounted on the top end of the stationary axis 316 and a top magnet 324 mounted on the top cover 322 of a case 320. By repelling the thrust magnet 326 mutually by the thrust magnet 318 and the top magnet 324, the rotor is floated to hold it at a predetermined position. Thereby, a so-called dynamic pressure air bearing is constituted, making it possible to rotate the rotor fast and stably. The thrust magnet 326 of the rotor 314 is opposite to the top magnet 324 of the top cover 322 with a small gap, with the result that disengagement of the rotor from the stationary axis 316 is prevented.
However, since three magnets are required to float the rotor, the number of parts of the optical deflector 310 itself increases, resulting in a higher cost. Also, the case 320 requires the top cover 322 to mount the top magnet 324, boosting cost again. In addition, such a vertical placement of the three magnets in the vicinity of the top end of the stationary axis 316 makes it difficult to make the optical deflector 310 a flat construction, causing expansion of the optical deflector 310 itself in the axial direction.
On the other hand, in an optical deflector 340 shown in FIG. 16 (see Japanese Published Unexamined Patent Application No. Hei 5-249398), a ring-shaped groove 346 is provided in the circumference of a rotor yoke 344 secured to a rotary axis 342. By inserting, in the groove 346 in a not-contacted manner, one end of an anchoring member 350 provided in a housing 348, disengagement of a rotary member is prevented.
In an optical deflector shown in FIG. 17 (see Japanese Published Unexamined Patent Application No. Hei 6-165428), disengagement of a rotor is prevented by a disengagement prevention plate 386 mounted between a polygon mirror 382 and a rotor magnet 384.
However, since these optical deflectors 340 and 380 rotatably hold a rotating member by a so-called dynamic fluid bearing, it is difficult to rotate a rotating member at high speed, in comparison with the optical deflector 310 employing a dynamic airbearing shown in FIG. 15. In the case of the dynamic fluid bearing, when the optical deflectors 340 and 380 are, for example, horizontally, obliquely, or inversely placed, to prevent possible leak of lubricating fluid, the dynamic fluid bearing must be sealed in the circumference thereof, making the construction complicated.
Furthermore, since the dynamic fluid bearing constructionally requires that a mechanism for disengagement prevention be provided in the vicinity (a portion larger the diameter) of the outer circumference of a rotating member, contact between the anchoring member 350 and the ring-shaped groove 346 in the optical deflector 340 shown in FIG. 16 might cause so-called rotation unbalance in the rotating member.